What is "Disk0s3"?

Specs :

- MacBook Pro 2.16 Core Duo 120GB HD

I reformatted my HD today, choosing to erase everything and return my MBP to 'all-stock' condition. Once all was said and done, I noticed that, out of 120 GB I only had 89 available. That didn't make sense to me so I went rooting around and...

in Disk Utility I found an un-mountable "Disk0s3" :

- Mount Point : Not Mounted
- Partition Type : Microsoft Basic Data (?!?!)
- Capacity : 10.5 GB

Well, I'm not using ANYTHING Windows. I can't imagine a reason this should be here, and I don't ever remember noticing it before. I'm sure Disk0s3 is common, but I can't find any website that just EXPLAINS what it is and how to 'fool around' with it.

Was I blind all along and it's some necessary partition, or what the BLEEP happened and how do I get my 10.5 gigs back?

THANKS!

The '0' refers to your boot drive and the 3 refers to the 3rd partition.
This is the standard listing for a windows partition installed under Boot Camp.

In terminal you can type in "diskutil list" without the quotes and you will see something like this:

/dev/disk0
#: type name size identifier
0: GUID_partition_scheme *111.8 GB disk0
1: EFI 200.0 MB disk0s1
2: Apple_HFS Macintosh HD 91.0 GB disk0s2
3: Microsoft Basic Data Untitled 20.5 GB disk0s3

and a bunch more.

While fairly competent in windows, am still pretty much a newb myself when it comes to this stuff on the Mac.
I know Boot Camp has the option of restoring the drive to a single partition. There should be an option to do this during a fresh install, but I have not done a fresh install yet, so I do not know what the partitioning options look like.

Maybe, someone else could shed some more light on how to go about it now.

My guess is:
1) probably another install (looking closely at the partitioning options). Would think there should be an option to delete all partitions and re-partition the drive into a single partition prior to formatting.
2) Or Drive Genius is suppose to be able to delete, move and resize partitions without data loss. Have not used this, so don't know if it will work if you formatted the windows partition as NTFS.
3) Or, maybe install Boot Camp and see if it will recognize the partition without having to re-install windows and give you the option of restoring the drive to a single partition.

I don't think it is aways the windows partition like it is in your case. Below is what I get:

/dev/disk0
#: type name size identifier
0: Apple_partition_scheme *465.8 GB disk0
1: Apple_partition_map 31.5 KB disk0s1
2: Apple_HFS Mac HD 465.6 GB disk0s3